1. Field of the Invention
The present invention relates to a radiation imaging apparatus and a radiation imaging system used for a medical diagnosis and an industrial non-destructive test, and a control method for the radiation imaging apparatus. The invention particularly relates to a radiation imaging apparatus and a radiation imaging system with which it is possible to detect the presence or absence of radiation irradiation such as start or end of radiation irradiation from a radiation generation apparatus, and a control method for the radiation imaging apparatus.
2. Description of the Related Art
A radiation imaging apparatus using a flat panel detector (which will be abbreviated as FPD) performs an imaging operation in synchronism with radiation irradiation by a radiation generation apparatus. As proposed in International Publication No. WO 2000/06582, the following technique may be used as a technique for this synchronization. A current that flows through bias wiring where bias is supplied to a conversion element is detected while a conductive state and a non-conductive state of a switch element are switched to detect the radiation irradiation by the radiation generation apparatus. An operation of the radiation imaging apparatus is controlled in accordance with a result of the detecting. According to this synchronization technique, as proposed in Japanese Patent Laid-Open No. 2010-268171, a problem may occur that noise generated at the time of switching the conductive state and the non-conductive state of the switch element affects the current that flows through the wiring where the bias is supplied to the conversion element to decrease an accuracy of the detecting. To reduce the influence of this noise, Japanese Patent Laid-Open No. 2010-268171 describes the following suggestions. A first suggestion is to provide a filter circuit between a current detecting unit and the bias wiring. A second suggestion is to provide a sample and hold circuit to an output terminal of the current detecting unit and perform processing of interrupting sample and hold at a timing of switching the conductive state and the non-conductive state of the switch element. A third suggestion is to perform differential processing of a noise waveform previously obtained and stored in a storage unit from the noise-affected current. A fourth suggestion is to align a timing of supplying the switch element with a non-conductive voltage for setting the switch element as the non-conductive state on a certain row with a timing of supplying the switch element with a conductive voltage for setting the switch element as the conductive state on another row to cancel the noise.
However, to detect the presence or absence of the radiation irradiation with a still higher instantaneousness and also at a high accuracy, the suggestions of Japanese Patent Laid-Open No. 2010-268171 are insufficient. According to the first suggestion, a problem of the detecting instantaneousness occurs since a band limitation of the filter circuit is set in accordance with a timing of the switching timing, and a delay is increased. According to the second suggestion, the problem of the detecting instantaneousness occurs since the detecting is not conducted until a resumption of the sample and hold in a case where the radiation irradiation is started during the interruption of the sample and hold. According to the third and fourth suggestions, a problem of the detecting accuracy occurs since variations in resistances and capacitances of wirings in a pixel array and variations in characteristics and performances of the switch elements cause variations in noise waveforms in a pixel array, and it is difficult to sufficiently reduce the noise influence.